Pressure-control valves (pilot- or spool-style) and sleeve- or pinch-type flow-control valves are often used in combination to regulate water-flow pressure in irrigation system conduits. In a pressure-reducing configuration, the pressure-control valve (hereinafter, the “spool valve”) is used to compare the downstream pressure in the conduit, i.e., on the downstream side of the flow-control valve (hereinafter the “control valve”), to a spring setting in the spool valve. If the force created by the downstream pressure (acting on an internal diaphragm in the spool valve) is greater than the spring setting, the internal spool will move to allow water to flow into the control valve to force an internal membrane in the control valve to move substantially radially inward toward a center valve seat to thereby constrict flow through the conduit until the downstream pressure is reduced. If the force created by the downstream pressure in the conduit is less than the spring setting, the internal spool will move to allow water to vent from the control valve, and thereby permit the membrane to move away from the seat to increase flow and downstream pressure. If the force created by the downstream pressure in the conduit is equal to the spring setting, then water flow will be blocked to and from the diaphragm-controlled chamber in the spool valve, thus creating a steady-state flow through the control valve. In this condition, the spool valve is said to be in equilibrium, or in a “null position”.
Currently, there are pumping systems that are susceptible to uncontrolled pressure oscillations or “cycling” between higher and lower pressures, particularly where there is compressibility in the system. Compressibility typically comes from air entrapped in the conduit. The likelihood of this condition increases as the flow rate decreases; as the incoming pressure increases; and/or as the differential between the incoming and outgoing pressure increases.
It would therefore be desirable to develop a pilot or spool-style pressure-control valve that either eliminates or substantially reduces pressure cycling in a water-flow-control valve while also improving accuracy and response time, particularly in agricultural irrigation applications where substantially constant water pressure is essential for the reliable and uniform application of water to specified areas, crops, etc.